Abstract
The Fluoride Ion Selective Electrode is an ion-selective sensor and will quickly and accurately measure fluoride ion activity rather than concentration in aqueous solutions. Fluoride ion activity depends on the solution total ionic strength and pH, and on fluoride complexing species. Adding an appropriate buffer provides a nearly uniform ionic strength background, adjust pH, and breaks up complexes so that, in effect, the electrode measures concentration. Pickling removes a thin surface layer from the stainless, using an acid solution, which is usually a hydrofluoric acid (HF) and nitric acid (HNO<sub>3</sub>), also called mixed acid. In this study, fluoride ion strength has been measured of pickling waste water from stainless steel by ion selective electrode. The results met the specification.
Highlights
Acid Cleaning (Pickling): Stainless steel is composed of iron (Fe), nickel (Ni), chromium (Cr) and several other minor components
The corrosion resistance of stainless steel depends on the formation of a ‘passive surface film’ composed of nickel and chromium oxides (Cr2O3&NiO)
The electrode is designed for the detection of fluoride ions (F-) in aqueous solutions and is suitable for use in both field any laboratory applications
Summary
Acid Cleaning (Pickling): Stainless steel is composed of iron (Fe), nickel (Ni), chromium (Cr) and several other minor components. Stainless steel is not resistant to chemical or physical attack. The corrosion resistance of stainless steel depends on the formation of a ‘passive surface film’ composed of nickel and chromium oxides (Cr2O3&NiO). Pickling is the most common chemical procedure used to remove oxides and iron contamination. Besides removing the surface layer by controlled corrosion, pickling selectively removes the least corrosion-resistant areas such as the chromium-depleted zones. Pickling normally involves using an inorganic acid mixture containing nitric acid (HNO3), hydrofluoric acid (HF) and, sometimes, sulfuric acid (H2SO4). Pickling solution remove contaminants such as ferrous and ferric oxide particles. Pickling involves metal removal and a charge or dulling in the visual brightness of the metal
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